feat(desktop): view-once image attachments (sender toggle + recipient lightbox + tombstone)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src/pages/ConversationPage.tsx

@@ -15,6 +15,7 @@ import {
   ArrowRightIcon,
   ChevronDownIcon,
   ChevronUpIcon,
+  EyeOffIcon,
   PlusIcon,
   PollIcon,
   ReplyIcon,
@@ -183,6 +184,10 @@ export function ConversationPage() {
   const [mentionState, setMentionState] = useState<{ query: string; start: number } | null>(null);
   const [emojiOpen, setEmojiOpen] = useState(false);
   const [gifPickerOpen, setGifPickerOpen] = useState(false);
+  // Sticky toggle: when on, the next image(s) sent are marked view-once.
+  // Auto-clears on a successful send so the composer doesn't accidentally
+  // burn the message-after-next.
+  const [viewOnceNext, setViewOnceNext] = useState(false);
   const pins = usePinnedMessages(id);
   const [pinnedPanelOpen, setPinnedPanelOpen] = useState(false);
   const pinnedIds = useMemo(() => new Set(pins.map((p) => p.messageId)), [pins]);
@@ -536,10 +541,13 @@ export function ConversationPage() {
     setSending(true);
     setSendError(null);
     try {
-      await send(text, attachments, replyTo?.id ?? null);
+      await send(text, attachments, replyTo?.id ?? null, { viewOnce: viewOnceNext });
       setText('');
       setAttachments([]);
       setReplyTo(null);
+      // Reset the sticky view-once flag so it only applies to the message
+      // the user explicitly armed it for — Snapchat / WhatsApp parity.
+      setViewOnceNext(false);
       if (fileInputRef.current) fileInputRef.current.value = '';
       setStickToBottom(true);
       notifyStopTyping();
@@ -1012,6 +1020,20 @@ export function ConversationPage() {
               onPick={(gif) => void handleGifPick(gif)}
             />
           </div>
+          <button
+            type="button"
+            onClick={() => setViewOnceNext((v) => !v)}
+            aria-pressed={viewOnceNext}
+            title={viewOnceNext ? 'Nächstes Bild: einmal ansehen' : 'Nächstes Bild: normal'}
+            className={
+              'flex h-9 w-9 cursor-pointer items-center justify-center rounded-md transition ' +
+              (viewOnceNext
+                ? 'bg-accent/20 text-accent'
+                : 'text-fg-muted hover:bg-surface-3 hover:text-fg')
+            }
+          >
+            <EyeOffIcon className="h-4 w-4" />
+          </button>
           <VoiceRecorder
             disabled={sending}
             onComplete={async (file) => {